Method of forming clad metal



G. R. LOHMAN METHOD OF FORMING CLAD METAL Filed June 12, 1964 Sept. 27, I966 United States Patent 3,274,681 METHOD OF FORMING CLAD METAL Gordon R. Lohman, Glen Ellyn, 111., assignor to Amsted Industries Incorporated, Chicago, 111., a corporation of New Jersey Filed June 12, 1964, Ser. No. 374,703 6 Claims. (Cl. 29528) The present invention relates to a method of forming clad metal.

A broad object of the invention is to provide a method of cladding metal in which the cladding metal is applied to and welded to the core or base metal without the interfacing surfaces thereof being exposed to atmosphere at any time in the cladding operation, thereby preventing corrosion of the metals and forming a perfect weld therebetween.

Another object is to provide a clad metal having a core or base metal and a cladding metal bonded thereto in which, in the operation of producing it, one of the metals, while initially in molten form, is permitted to at least partially freeze whereby to form at least a semi-solid or rigid member and applying the other metal thereto in molten form, in which the surface of the first metal exposed to the second metal is at least partially molten, whereby upon contact therewith by the second metal, and subsequent freezing of both metals, a perfect bonding or Welding effect takes place between the two metals.

A further object of the invention is to utilize the physical phenomenon that a given air pressure will maintain a given height of molten metal, and to form a column of molten metal and permitting the outside portion of it at least to partially freeze, and thereafter pouring in a second molten metal which displaces the molten portion of the first metal by its own weight against the given air pressure maintaining the column, and thereby providing an accurate composite article having well-defined boundaries between the metal that is subsequently poured into the column and the first metal that is displaced thereby.

Other objects and advantages of the invention will appear from the following detailed description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a vertical sectional view of mold apparatus adapted for use in carrying out the method of the present invention;

FIGURE 2 is a view of the mold per se of FIGURE 1 showing the metals which are to form the cast product, in the mold;

FIGURE 3 is a cross-sectional View of an item cast according to the foregoing method, but with the different metals therein in exaggerated proportions and thickness; and

[FIGURE 4 is a diagrammatic illustration of a rolling operation.

Referring in detail to the drawings, attention is directed first to FIGURE 1 showing mold apparatus for use in carrying out the method of the invention. This mold apparatus includes a tank having a compressed air inlet conduit 12 and a compressed air outlet conduit 14 for connection with a suitable compressor or pump (not shown) utilized for providing the desired compressed air in the tank and including suitable controls for controlling the pressure therein and the release of it. The tank 10 in the casting operation is closed by a removable cover 16.

For the casting operation, a ladle 18 is placed in the tank, this ladle containing a quantity of cladding metal 20, the characteristics of which will be referred to herein below. A pouring tube 22 extends down from the cover 16 into the ladle to a position adjacent the bottom thereof and upon increase of air pressure in the tank, the cladding metal is forced upwardly through the tube and into the mold 24. The pouring tube 22, in itself of conven tional construction, is mounted in a suitable assembly 26 mounted on and secured to the cover 16. The assembly 26 may include a bottom plate 28 and another plate 30, the latter including a core element 32 forming an extension of the upper end of the pouring tube. The assembly 26 and the pouring tube 22 are carried with the cover 16 and removed from the tank upon removal of the cover, and of course replaced in position upon replacement of the cover.

The mold 24 is placed atop the assembly 26 and a shut-off slide 34 is interposed in position as, for example, in a slot in the lower end of the mold and resting on the top plate 30. This slide has a refractory insert or core 36 having an aperture registering with the passage in the pouring tube in an open position of the slide, which is that shown in FIGURE 1. The slide 34 is movable to an opposite and closed position, to the right of that shown, where a solid insert 38 is then in register with the pouring tube and shuts off the latter from the mold.

The mold 24 preferably includes a graphite member 40 defining a cavity 42 and encased, if desired, in a sheath or casing 34 which may be of metal. The graphic member 40 may include a lower portion 36 forming the main cavity of the mold and a riser 48 on top of the member 46 and having a riser hole 50 therein preferably of upwardly diverging shape. 7

A pouring ladle 52 is provided for the core or base metal 54, a quantity of such being shown therein, the pouring ladle having a pouring lip 56 for convenience in pouring the metal.

The two metals utilized in the cladding operation need not be any particular metals, but may be any of a wide variety thereof. In the present instance, examples of such metal may be stainless steel for the cladding metal, and carbon steel for the core metal. The uses to which clad metal can be put are numerous, and difficulties in cladding base steel with corrosion resisting metals are known. There are numerous conditions that cause the dilficulties, a principal one being exposure of the surfaces of the two metals that are to be welded together to atmosphere which results in serious corrosion of those surfaces and preventionvof effective welding therebetween. In the present instance, the exposure of those surfaces to atmosphere is avoided.

To perform the process, air pressure is introduced into the tank 10 and in response thereto the cladding metal 20 is forced up the pouring tube into the mold, with, of course, the shut-off gate in open position, as shown in FIGURE 1. When the cladding metal reaches the desired height which, in the present instance, may be at the top of the cavity 42, as indicated by the line 58, the pouring operation is terminated but the pressure in the tank is maintained, which holds the column of molten metal in the mold at the stated height.

The air pressure is maintained at the desired pressure until the metal in the mold chills and at least partially freezes at its circumference, forming a shell shown at 60 in FIGURE 2. The core metal 54 is then poured from the pouring ladle 52 into the riser 48 in such a manner as to eliminate or at least minimize disturbance of the two metals, and the boundary between the two metals is substantially a plane.

Due to the fact that a given pressure in the tank will maintain a given height ofmetal in the mold, pouring the metal into the mold results in a constant height or head of the molten metal in the mold, in response to the maintenance of the desired air pressure in the tank. Continued pouring of the core metal forces the middle portion or core of the cladding metal downwardly, as indi- 3 cated by the dot-dash line 62 (FIG. 2), which represents an intermediate stage in the pouring operation. Further pouring of the core metal 54 results in continued lowering or sinking of the latter and of the boundary between the two metals, i.e. the line 62.

The boundary between the two metals progresses to a position according to the amount of core metal poured into the mold, and this can be, and under the present invention preferably is, determined by accurate calculation of the amount of core metal poured into the mold, corresponding to the size of the mold and other factors such as time permitted for cooling, etc. When the boundary between the metals then progresses to the desired level, namely at or in the shut-off slide plate 34, the pouring of the core metal is terminated and the column of molten metal, or the two molten metals, in the mold remains stationary. Then the shut-off slide plate is moved to shut-01f position, i.e. moved to the right, as viewed in FIGURE 1, and thereafter other steps are taken such as releasing the pressure from the tank and removing the mold from the tank. The molten metal in the mold is then permitted to solidify, and the cast product or billet is removed therefrom and treated as ex-.. plained herein below.

The thickness of the shell of the clad metal 60 is determined by the length of time that the clad metal remains in the mold before pouring in the core metal, together with other factors such as size of the mold, etc. These factors are easily calculable so that a shell of desired thickness is produced. While the dimensions of the various elements and components of the apparatus involved herein and described above may be as desired, certain examples are given below for convenience in teaching the practice of the invention. In a practical operation of the invention, a mold 24 was used which had a cavity 3" x 9 /2 x 90" high up to the line 58. The cladding metal was poured into the cavity by air pressure in the tank and held therein for approximately 10 seconds. Thereafter the core metal was poured during a period of approximately 30 seconds, and in this latter period the center molten portion of the cladding metal was forced downwardly by the core metal. In such operation a shell 60 was formed of a thickness of in the neighborhood of 0.2". The metals used were 18-8 stainless steel for cladding metal, and the core metal was 1010 carbon steel. The cladding stainless steel was heated to in the neighborhood of 2850 F., and the core metal to about 2900 F.

The billet thus formed is represented in FIGURE 3, but as noted above the thicknesses and proportions represented in this figure are exaggerated. This figure illustrates a billet 64 having a core 66 made of core metal 54 of carbon steel and a clad coating 68' of stainless steel 20. This billet is then rolled as represented in FIGURE 4 by a series of rollers 70 to a thickness of in the neighborhood of .020". This results in a clad coating of in the neighborhood of .0013" in thickness. It has been found that a clad coating of this thickness is satisfactoryfor a wide variety of purposes, such as provided by other kinds of processes. In the rolling operation the clad coating forms an extremely uniform film which is nonporous and extremely solid, and bonded to the core metal in a perfect weld, without any corrosion on the interfacing surfaces of the two metals.

It will be understood that not only can the billet or cast article be of any desired dimensions, but the thickness of the clad coating in proportion to the whole product can be as desired, according to the length of time that the metal is permitted to rest in the mold before the core metal is introduced thereinto.

While I have shown and described herein a certain preferred form of the invention, it will be understood that changes may be made therein within the scope of the appended claims.

I claim:

1. A method of cladding metal in a mold open at both ends comprising the steps of introducing a quantity of molten cladding metal up into the mold through the bottom opening thereof to achieve a predetermined interface level with the atmosphere by applying fluid pressure to a reservoir of said molten cladding metal, retaining the cladding metal in the mold by maintaining said fluid pressure until a surface portion freezes and forms a shell, displacing the remaining molten portion of the cladding metal downwardly from the central portion of the mold by introducing molten core metal into the mold through the top opening thereof against said fluid pressure while maintaining said atmosphere/molten metal interface level in the mold, and permitting said core metal to freeze to produce a solidified body after all the remaining molten cladding metal has been displaced.

2. A method of producing a clad metal sheet comprising forming a billet according to the method of claim 1 and thereafter rolling the billet into a thin sheet in an operation that reduces the thickness of the core metal and cladding metal proportionately.

3. A method as set out in claim 1 wherein the core metal is a low-corrosion-resistant metal, and the cladding metal is a high-corrosion-resistant metal, and both metals have a high proportion of a common elements as to provide a tight weld.

4. The method set out in claim 1 in which said fluid pressure is supplied by a means for applying air under pressure to said cladding metal reservoir.

5. The method set out in claim 4 with the further step of calculating the amount of core metal poured into the mold and so pouring only that amount as to displace the central molten portion of the cladding metal to a depth not exceeding the lower end of the mold cavity.

6. The method set out in claim 5 in conjunction with the further step of shutting off the mold from the means for producing the air pressure therebelow, and removing the mold from the last named means, and thereafter removing the cast product from the mold.

References Cited by the Examiner UNITED STATES PATENTS 1/1962 Strom et al. 22-69 7/1965 Sylvester 22-60 

1. A METHOD OF CLADDING METAL IN A MOLD OPEN AT BOTH ENDS COMPRISING THE STEPS OF INTRODUCING A QUANTITY OF MOLTEN CLADDING METAL UP INTO THE MOLD THROUGH THE BOTTOM OPENING THEREOF TO ACHIEVE A PREDETERMINED INTERFACE LEVEL WITH THE ATMOSPHERE BY APPLYING FLUID PRESSURE TO A RESERVIOR OF SAID MOLTEN CLADDING METAL, RETAINING THE CLADDING METAL IN THE MOLD BY MAINTAINING SAID FLUID PRESSURE UNTIL A SURFACE PORTION FREEZES AND FORMS A SHELL, DISPLACING THE REMAINING MOLTEN PORTION OF THE CLADDING METAL DOWNWARDLY FROM THE CENTRAL PORTION OF THE MOLD BY INTRODUCING MOLTEN CORE METAL INTO THE MOLD THROUGH THE TOP OPENING THEREOF AGAINST SAID FLUID PRESSURE WHILE MAINTAINING SAID ATMOSPHERE/MOLTEN METAL INTERFACE LEVEL IN THE MOLD, AND PERMITTING SAID CORE METAL TO FREEZE TO PRODUCE A SOLIDIFIED BODY AFTER ALL THE REMAINING MOLTEN CLADDING METAL HAS BEEN DISPLACED.
 2. A METHOD OF PRODUCING A CLAD METAL SHEET COMPRISING FORMING A BILLET ACCORDING TO THE METHOD OF CLAIM 1 AND THEREAFTER ROLLING THE BILLET INTO A THIN SHEET IN AN OPERATION THAT REDUCES THE THICKNESS OF THE CORE METAL AND CLADDING METAL PROPORTIONATELY. 